The present invention generally pertains to radiation seekers for guided missiles and is particularly directed to an improvement in look angle sensors for use in such radiation seekers.
Radiation seekers are an integral part of some missile guidance systems. In some guided missiles, infrared (IR) radiation seekers are employed to detect the position of a target. In order for the radiation seeker to determine the direction of the target in relation to the trajectory of the missile it is necessary to ascertain the look angle of the IR radiation seeker.
In guided missiles to which a roll is imparted to the airframe while in flight, the IR radiation seeker includes an optical system that is secured to a gimbal housing that is stationary with respect to the missile airframe. The gimbal ring is adapted for rotating back and forth relative to the airframe during a missile roll cycle when the look angle of the IR radiation seeker relative .to the airframe is not zero degrees.
A look angle sensor is coupled to the optical system of the IR radiation seeker for providing a look angle signal that indicates the look angle of the IR radiation seeker. The look angle signal has an amplitude that is proportional to the look angle, a relative phase that indicates the direction of the look angle and a frequency that is equal to the roll frequency of the missile. In some missile guidance systems, the look angle signal is compared to a signal that is obtained from a radio frequency (RF) radiation antenna that is secured to the missile airframe in a fixed position in order to produce an error signal that is used to guide the missile toward the source of the IR radiation.
A typical prior art look angle sensor that is used for providing a signal to indicate the look angle of an IR radiation seeker in a rolling airframe guided missile includes a potentiometer having a resistance pickoff wiper contact that is coupled to the movable portion of the optical system of the IR radiation seeker. Such a look angle sensor does not always provide a consistently reliable performance because of variations in the pressure of the wiper contact within the potentiometer. When the wiper pressure is too low, the accuracy of the picked-off resistance value degrades in time due to wear of the wiper contact. When the wiper pressure is too high, there is a drift in the signal that is produced.
It is an object of the present invention to provide an accurate and consistently reliable radiation seeker look angle sensor that does not include any variable contacting elements, such as the wiper contact of a potentiometer.